Our laboratory has continued investigating the molecular mechanism of the antiviral effects of polyanionic compounds and the role of cell surface proteoglycans in mediating HIV-1 infection. Our results have revealed that the inhibitory effects of polyanionic polysaccharides on viral binding, viral replication and syncytia formation are mediated by interactions with the V3 principle neutralizing domain of gpl20 and with envelope regions near the CD4 binding site. We have also identified a cell surface sulfated polysaccharide, heparan sulfate proteoglycan, as a novel HIV binding site on the T-cell surface which functions together with CD4 to mediate HIV entry. We have biochemically identified proteoglycan synthesis in HIV susceptible T-cell lines and have demonstrated by enzymatic treatment of T-cell lines with heparitinase and by inhibition of glycosaminoglycan sulfation that heparan sulfate is required for HIV-1 infection. We have quantitated direct virus binding to cells and have found that treatment of cells with heparitinase inhibits HIV-1 binding to the T-cell surface. Exogenous HS added to cultures inhibited virus infection in a manner analogous to dextran sulfate, further supporting a functional role for HS in HIV-1 binding. These results provide direct evidence for participation of cell surface heparan sulfate proteoglycans in HIV-cell attachment and virus entry. The description of this new cell entry site potentially should allow for additional modes of antiviral therapies.